When a wave propagating on a string gets reflected from a fixed rigid support,what is the change in its phase?

Two waves are approaching each other with a velocity of $16 \ m/s$ and frequency $n$. The distance between two consecutive nodes is

$A$ string of length $0.5 \text{ m}$ and mass $10^{-3} \text{ kg}$ is tightly clamped at its ends. The tension in the string is $0.8 \text{ N}$. Identical wave pulses are produced at one end at equal intervals of time $\Delta t$. What is the minimum value of $\Delta t$ which allows constructive interference between successive pulses (in $\text{ s}$)?

The equation $y = 0.15 \sin(5x) \cos(300t)$ describes a stationary wave. The wavelength of the stationary wave is .... $m$.

The equation of a stationary wave is $y = 0.8 \cos \left( \frac{\pi x}{20} \right) \sin (200 \pi t)$,where $x$ is in $cm$ and $t$ is in $sec$. The separation between consecutive nodes will be .... $cm$.

The equation of a stationary wave along a stretched string is given by $y = 5 \sin \frac{\pi x}{3} \cos 40\pi t$,where $x$ and $y$ are in $cm$ and $t$ is in seconds. The separation between two adjacent nodes is..... $cm$.